The present invention relates to a receiving device or a reproducing device provided in an information transmitting and communicating apparatus or an information storing and reproducing apparatus, and more particularly to a maximum likelihood decoding device or a method of implementing a general composition of a maximum likelihood decoding circuit widely uses in various information processing and signal processing devices.
In order to improve low-quality transmission or reliability of data reproduction from a recording and reproducing signal in a fast information communications system or a high-density information recording and reproducing system, there has been widely used an error correction demodulation technique based on a data decoding technique and a convolutional encoding technique that utilizes the MLSD (Maximum Likelihood Sequence Detection).
This maximum likelihood sequence detection is a technique of suppressing a probability of causing an error in a decoded code sequence to a minimum by estimating the decoded code sequence in time series based on the storage characteristic or the correlation of the decoded data. In this technique, when a received signal sequence {Y(n)} (n denotes an integer for indicating a discrete signal occurrence sequence and time) is given into the decoding input, the maximum likelihood sequence of receiving {Y(n)} (the maximum likelihood sequence) is selected from all possible transmission information (code) sequences {X(n)} and then the maximum likelihood sequence is outputted as the decoded information (code) sequence {Z(n)}. In other words, given all possible sequences of a certain receiving signal sequence {Y(n)}, on the assumption of a certain transmitting sequence {X(n)}, the transmitting sequence {X(n)} is selected so that the a-posterior probability P ({Y(n)}/{X(n)}) before and after the receiving signal sequence {Y(n)} is received is made maximum, for estimating the maximum likelihood sequence of the decoded sequence {Z(n)}. At this time, the transmitting sequence {X(n)} is estimated not independently but in context. This kind of maximum likelihood sequence detection provides the most excellent decoding error probability in the decoding operation as keeping a correct decision probability P ({X(n)} & {Z(n)}) (the probability of coinciding the transmitting sequence {X(n)} with the decoded sequence {(Z(n)}) in the condition of transmitting all possible transmission sequences {X(n)} at equal probabilities, in other words, in the condition of giving no information about the transmitting probability of each transmitting sequence {X(n)}.
This maximum likelihood sequence detection is efficiently realized by using a dynamically programming Viterbi algorithm. Papers about the maximum likelihood sequence detection and the Viterbi algorithm include, for example, G. D. Forney, "The Viterbi Algorithm", Proceedings of the IEEE, vol. 61, No. 3, March 1973, pp. 268 to 278 and G. Ungerbock, "Adaptive Maximum Likelihood Receiver for Carrier-Modulated Data Transmission Systems", IEEE Transactions on Communications, vol. COM-22, No. 5, May 1974, pp. 624 to 638. These papers discuss the receiver apparatus arranged to use the maximum likelihood sequence detection or its partial basic arrangement. Further, the actual implementation of the Viterbi Algorithm is discussed in detail in Hui-Ling Lou, "Implementing the Viterbi Algorithm", IEEE Signal Processing Magazine, September 1995, pp. 42-52 and G. Fettweis and H. Meyr, "High-speed Parallel Viterbi Decoding: Algorithm and VLSI-architecture", IEEE Communications Magazine, May 1991, pp. 46 to 55.